Mobile wireless communication devices, such as a cellular telephone or a wireless personal digital assistant, can provide a wide variety of communication services including, for example, voice communication, text messaging, internet browsing, and electronic mail. Mobile wireless communication devices can operate in a wireless communication network of overlapping “cells”, each cell providing a geographic area of wireless signal coverage that extends from a radio network subsystem (RNS) located in the cell. The radio network subsystem can include a base transceiver station (BTS) in a Global System for Communications (GSM) network or a Node B in a Universal Mobile Telecommunications System (UMTS) network. Whether idle or actively connected, a mobile wireless communication device can be associated with a “serving” cell in a wireless communication network and be aware of neighbor cells to which the mobile wireless communication device can also associate.
Mobile wireless communication devices can support both voice and data connections, in some cases simultaneously, through radio resources allocated by the radio network subsystem located in the cell. The allocated radio resources can determine a portion of the radio frequency spectrum that the mobile wireless communication device can use when transmitting and receiving signals over a radio access portion of the wireless communication network. Multiple simultaneous data connections between the mobile wireless communication device and the wireless communication network can also be supported. The voice and data connections can include paths through circuit switched and/or packet switched domains of a core network that interconnects the mobile wireless communication device to a public switched telephone network (PSTN) and/or a public data network (PDN). Radio resources in the wireless access network can be limited, with multiple mobile wireless communication devices sharing an uplink connection to the wireless access network using frequency division, time division, code division multiplexing methods or a combination thereof. The wireless access network can limit the maximum transmit power at which a mobile wireless device can transmit in order to minimize interference between the multiple mobile wireless communication devices sharing the uplink connections.
Within the maximum transmit power limit specified by the wireless access network, a mobile wireless communication device can determine a combination of voice and data packets to transmit to the wireless access network during a transmit time interval. The combination of voice and data packets used and properties of the packet's formats on a transport channel can be communicated to the wireless access network using a transport format combination indicator. The wireless communication network can provide to the mobile wireless communication device a set of transport format combinations that can be used. Each permissible transport format combination can be specified by one of the transport format combination indicators.
As higher rate data packets can require more transmit power than lower rate voice packets, when the mobile wireless communication device transmits, the mobile wireless communication device can select a transport format combination that balances transmit power with packet prioritization. When the mobile wireless communication device transmits at maximum transmit power, all of the transport format combinations that include data transmissions can require a higher transmit power than can be available. Transmitting data at a lower transmit power than required can result in higher data packet error rates, and ultimately a reset of the data connection can occur. Consequently all other simultaneous connections between the mobile wireless communication device and the wireless access network, such as a voice connection, can also be severed when the data connection is reset. This can result in an undesirable call drop between the mobile wireless communication device and the wireless access network.
Thus there exists a need to modify transport format selection to account for transmit power levels and for a mixture of voice and data packets to maintain a stable connection between the mobile wireless communication device and the wireless access network.